A flexible polyurethane foam having a low rebound resilience i.e. low resiliency, has been widely used for a shock absorber, a sound absorbent or a vibration absorber for e.g. automobiles, electronic instruments, etc. Such a flexible polyurethane foam is required to have not only the low resiliency but also high air flow to facilitate dissipation of heat.
Further, as a flexible polyurethane foam to be used for such applications, a hot press molded product obtained by hot press molding a flexible polyurethane foam obtained by a reaction of a polyol with a polyisocyanate, has been widely used, since it can easily be molded to have an optionally set density and thickness.
As a low resilience flexible polyurethane foam, Patent Document 1 discloses a low resilience flexible polyurethane foam obtained by reacting a specific polyol with a polyisocyanate.
However, the flexible polyurethane foam as disclosed in Patent Document 1 is inadequate in hot moldability. Therefore, in order to obtain a desired density and thickness by hot press molding of the obtained flexible polyurethane foam, it is obliged to carry out hot press molding at a high temperature for a long time. Consequently, the obtainable hot press molded product is likely to have problems such as a discoloration and deterioration in the durability, air flow, etc.
Further, the following methods are disclosed as methods for improving hot moldability of flexible polyurethane foams.
A method of using a special additive such as an aliphatic monocarboxylic acid, a compound to block an isocyanate group or a cooling agent (Patent Documents 2 to 4), a method of using a trimerization catalyst (Patent Documents 5 to 7) and a method of using a modified isocyanate such as allophanate isocyanate and blocked isocyanate (Patent Documents 4 and 8).
However, by such methods, it is difficult to sufficiently impart hot moldability to a flexible polyurethane foam while maintaining excellent low resiliency and air flow. Therefore, it is desired to develop a process for producing a flexible polyurethane foam which is excellent in low resiliency, air flow and hot moldability.
Patent Document 1: WO06/115169
Patent Document 2: JP-A-7-2968
Patent Document 3: JP-A-6-329753
Patent Document 4: JP-A-2007-91836
Patent Document 5: JP-A-2004-182927
Patent Document 6: JP-A-2006-213896
Patent Document 7: JP-A-4-246429
Patent Document 8: JP-A-7-118362